The invention generally relates to a confocal imaging system, preferably for the generation of height values or height images.
Height images can be recorded in the microscopic range by using confocal microscopy. In order to carry out the variation of the optical path length necessary for this, according to the prior art the front objective is moved to and fro in the direction of the optical path length. The data rate which can be achieved in this case, however, is restricted to a few 100 Hz.
Patent Specification DE 196 08 468 C2 discloses a system in which the variation of the optical path distance is varied on the image side through the oscillation of a receiver or of an interposed deviating mirror. With the use of a deviating reflector, the mass to be moved is reduced to a few milligrams and the deflection is simultaneously doubled. In comparison with the oscillation of a front objective, it is thereby possible to achieve data rates which are about ten times higher. The oscillation movement is brought about through an electromagnetically driven resonance oscillator. In conjunction with a parallel layout of the overall confocal system, for example 32 times, data rates of up to 200 kHz are thereby achieved.
A substantially higher data rate is required in many industrial applications. This is true, in particular, of automatic inspection in electronics fabrication. The extent to which an electromagnetically drivable oscillator at about 2 kHz can provide a sufficient data rate is therefore crucial.
A problem with the described system involves the strong sound emission. This is scarcely avoidable in the case of electromagnetic drives at the amplitudes and frequencies still necessary here.
It is an object of an embodiment of the invention to optimize confocal imaging systems with respect to their data rate and reliability.
The discovery of an embodiment of the invention involves separating the mutually connected mirrors used previously, so as to provide separate micromirrors which are likewise set at 90xc2x0 with respect to one another. Embodiment as micromirrors reduces the mass to be set in oscillation. The drive may be electrostatic. The achievable frequencies are substantially higher than according to the prior art, for example 10 kHz or higher.
The micromirrors are preferably formed integrally in silicon together with a spring suspension. Besides the relatively low oscillation energy in combination with the smaller surface areas, the sound emission is substantially reduced. Crystalline silicon furthermore constitutes an ideal spring material. The life of the mechanical oscillator can thereby be extended significantly in comparison with electromagnetic drives, and the hysteresis of the displacement/time response is substantially improved.